Process for making aluminosilicate for record material

ABSTRACT

A process for the production of an aluminosilicate containing at least 9 weight percent alumina, having a BET surface area of 300-600 m 2  /g, and an average pore volume of of 0.2-0.5 ml/g is disclosed. The process includes the steps of preparing an aqueous solution comprising at least one metal silicate, adjusting the pH of said aqueous solution comprising at least one metal silicate with a sufficient amount of an aqueous solution comprising at least one aluminum salt to produce an aqueous solution having a pH of 4.4-7.7, precipitating aluminosilicate from the aqueous solution by concurrently dosing additional aqueous solution comprising at least one metal silicate in such a manner such that the pH is maintained at 4.4-7.7, steps (a)-(c) being carried out at a temperature of 0°-80° C. and isolating said aluminosilicate. The aluminosilicate is useful as a pressure sensitive pigment in carbonless copy paper.

FIELD OF THE INVENTION

The present invention relates to a process for the production ofaluminosilicates and to particular aluminosilicates having a highsurface area and alumina content which are produced therefrom.

BACKGROUND OF THE INVENTION

Aluminosilicates useful in copy paper are known from Belgian patentpublication 812,140. These aluminosilicates have a surface area of300-800 m² /g, an average pore volume of 0.5-1 ml/g, an average particlediameter of 3-15 μm, and an alumina content of 7.5-28% by weight. Alsodisclosed is a process for the production of aluminosilicates whichconsists of reacting aluminum sulphate and sodium silicate in solution.

U.S. Pat. No. 3,915,734 discloses a sodium aluminosilicate useful aspigments in paper coatings, as fillers in rubber compounds, in inks,paints, plastics and the like. The reaction mixture from which thealuminosilicate is obtained includes an alkali metal silicate, analuminum salt, and alkaline earth metal salt. The use of a reactionmixture not containing an alkaline earth metal salt in a similar processis mentioned in U.S. Pat. No. 2,739,073.

In a preferred process of U.S. Pat. No. 3,915,734, a portion of thesolution of the alkali metal silicate, e.g., sodium meta- or disilicate,is added to the reaction media prior to the introduction of the aluminumsalt solution, e.g., aluminum sulphate. In general, the pH should bemaintained at 8-12 until all of the alkali metal silicate has beenadded. The addition of the aluminum salt solution may then be continueduntil the pH is reduced to 8-10. The temperature of the reaction vesselis maintained at 65° C. throughout the reaction. In Example 4 thealuminum sulphate and sodium silicate solution are added simultaneouslywhile the pH is maintained at 8.0 by adjusting the rate of addition ofthe two solutions.

The process disclosed in U.S. Pat. No. 3,915,734 differs from thepresent process in one important respect: the precipitation must becarried out at a pH from 8.0-10.0. This difference is critical since thepH at which precipitation is carried out exerts a strong influence onthe properties of the aluminosilicate product.

British patent publication 1,477,557 discloses an aluminosilicate havinga surface area of 185-622 m² /gram. A process for making the sameconsists of mixing at high shear rate concentrated aqueous solutions ofalkali metal silicate such as sodium silicate and of a metal salt otherthan an alkali or alkaline earth metal such as aluminum sulphate. The pHof the resulting aqueous composition is from 2-7.5. Preferably, thealkali metal silicate is sodium silicate and the metal salt is aluminiumsulphate. These aluminosilicates can be used in water purification, asfillers in paper and textiles, as coatings for filaments and fibres insynthetic textiles, in the compression moulding industry, in waterdesalination, and as a filler in soap.

The process of the British patent publication differs from the presentprocess in that it employs a far higher ratio of SiO₂ :Na₂ O than isused in the present process. Further, this patent does not have as aprimary goal the production of high surface area products and thusstates that equally good results are obtained at pH 2.5-3.5 as at pH5.0-6.0 whereas in the present process, pH 2.5-3.5 cannot besuccessfully employed.

International patent publication WO 8,103,642 describes a recordmaterial carrying a colour developer composition comprising a hydratedsilica/hydrated alumina composite. A process for making the coatedrecord material consists of reacting hydrated silica and hydratedalumina together in an aqueous medium to produce a dispersion of saidcomposite, applying a coating composition incorporating said compositeto a substrate and drying the coated substrate to produce said recordmaterial, characterized in that the mean alumina content of thecomposite on a dried weight basis is up to 7.5%. For example thecomposite can be prepared by adding together sodium silicate andaluminium sulphate solution, and subsequently reducing the pH to 7.0 byaddition of sulphuric acid.

In JO 2221-113, JO 3193-620, and JO 3193-621 a process for theproduction of aluminosilicate mullite precursors is disclosed. In theprocess, solutions of aluminum salt and alkali metal silicate areprovided to the reaction zone and reacted at a temperature above 80° C.at a pH of 4-10.

European patent application publication 434 306 discloses a process forthe production of aluminosilicates and the use of these aluminosilicatesin carbonless copy paper. In this process, an acid aluminum saltsolution is prepared and then metal silicate solution is added theretountil the pH is 4.0 and aluminosilicate begins to precipitate. Then, thesolution is further alkalified with a strong base to a pH of 7 to inducefurther precipitation of aluminosilicate and separating thealuminosilicate from the reaction media. Notable is that this processrequires an additional hydrothermal treatment of the aluminosilicate gelto produce an acceptable product.

The foregoing processes are all suitable for the production ofaluminosilicates. However, large variations in the properties of thesealuminosilicates are observed when employing these processes.Accordingly, there is a need in the art for a well-definedaluminosilicate production process which provides aluminosilicateshaving a high alumina content, a high surface area and consistentproperties. These aluminosilicates are suitable for the production ofrecord materials such as carbonless copy paper.

It is the primary object of the present invention to provide awell-defined aluminosilicate production process which provides aconsistent, high quality aluminosilicate with a high alumina content anda high surface area. It is a further object of the present invention toprovide a particular aluminosilicate product which is suitable for usein carbonless copy paper, among other applications. These and otherobjects of the invention will be apparent from the summary and detaileddescription which follow.

SUMMARY OF THE INVENTION

The present invention relates to a process for the production of analuminosilicate containing at least 9 weight percent alumina, having aBET surface area of 300-600 m² /g, and an average pore volume of 0.2-0.5ml/g. The process comprises the steps of:

a) preparing an aqueous solution comprising at least one metal silicateand having an SiO2:metal oxide molar ratio of 2.8-3.5;

b) adjusting the pH of said aqueous solution comprising at least onemetal silicate with a sufficient amount of an aqueous solutioncomprising at least one aluminum salt to produce an aqueous solutionhaving a pH of 4.4-7.7;

c) precipitating aluminosilicate from the aqueous solution of step (b)by concurrently dosing additional aqueous solution comprising at leastone metal silicate and having an SiO2:metal oxide molar ratio of2.8-3.5, and additional aqueous solution comprising at least onealuminum salt to the aqueous solution of step (b) in such a manner suchthat the pH is maintained at 4.4-7.7, steps (a)-(c) being carried out ata temperature of 0°-80° C.; and

d) isolating said aluminosilicate.

In a second aspect, the present invention relates to an aluminosilicatecharacterized in that it contains at least 9 weight percent alumina, andit has a BET surface area of 300-600 m² /g, and an average pore volumeof of 0.2-0.5 ml/g. In a third aspect, the present invention relates tothe use of this aluminosilicate in carbonless copy paper (also known aspressure-sensitive record material).

BRIEF DESCRTPTTON OF THE DRAWING

FIG. 1 is a plot of the pore volume and surface area of thealuminosilicate products against the pH at which the precipitationreaction is carried out.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

In the first step of the present process, an aqueous solution of atleast one metal silicate is prepared. This aqueous solution has an SiO₂:metal oxide molar ratio of 2.8-3.5, and, more preferably, 3.0-3.4. Thesolution generally has a solids content in the range of 0.1-20% and morepreferably in the range of 1-10% by weight of the total solution.Particularly preferred solids contents are from 2-5% by weight. Suchsolutions are commercially available, but generally having a solidscontent of 35-50%. A simple dilution of these higher solids solutionsgives a suitable starting solution for the present process.

The preferred metal silicate solution is a solution of sodium silicate.Other metal silicates can also be used such as potassium silicate, forinstance. The metal silicate solution, generally having a pH of 10-11,can be used as is in the process of the present invention or can bealkalified by addition of a strong base such as sodium hydroxide,thereby permitting a larger addition of acidic aluminum salt to themetalsilicate solution without lowering the pH to an undesirably lowlevel.

In the second step of the process, the pH of the metal silicate solutionis adjusted to 4.4-7.7 by addition of an acidic aluminum salt solutionthereto. The more preferred pH range is from 5.0-7.5, and most preferredis from 5.5-6.5. The quantity of aluminum salt solution required willdepend upon the initial pH of the metal silicate solution and whether itwas alkalified, as well as on the pH of the aluminum salt solution andthe pH desired for the particular reaction conditions. It is alsopossible to adjust the pH of the aluminum salt solution, for examplewith sulfuric acid, prior to its addition to the metal silicatesolution.

This pH adjustment step can also be performed by simultaneous additionof aluminum salt solution and additional metal silicate solution so longas the net result is a pH reduction of the metal silicate solution intothe desired pH range. In addition, some precipitation will be observedduring the pH adjustment step due to reaction of the aluminum salt withthe metal silicate.

The preferred aluminum salt solution is a solution of aluminum sulphate,although other aluminum salts can also be employed. The aluminum saltsolution is generally employed in a concentration of 3-20 percent Al₂ O₃by weight of the total solution, and more preferably in a concentrationof 5-15%.

The third step in the process of the- present invention is theprecipitation of aluminosilicate from the aqueous solution having a pHof 4.4-7.7 obtained from the second step in the process. Thealuminosilicate is precipitated by concurrently dosing additionalaluminum salt solution and additional metal silicate solution in such amanner as to maintain the pH of the reaction media at 4.4-7.7. The metalsilicate solution generally has a solids content in the range of 5-50%and more preferably in the range of 10-35% by weight of the totalsolution. Particularly preferred solid contents are from 20-30% byweight.

The preferred dosing method is the simultaneous dosing of metal silicateand aluminum salt solutions in amounts, relative to one another, thatwill maintain the pH in the desired range. Even more preferred is todose the metal silicate solution at a constant rate of 0.1-10 weightpercent per minute, based on the weight of the initial metal silicatesolution prepared in the first step of the process and to then adjustthe dosing rate of aluminum salt solution so as to maintain the pH inthe desired range. An even more preferred metal silicate dosing rate isfrom 0.5-5.0 weight percent per minute, based on the weight of theinitial metal silicate solution prepared in the first step of theprocess.

The first three steps of the process of the present invention arecarried out at a temperature of 0°-80° C. and more preferably at 20°-60°C. While the temperature has some influence on the properties of thefinal product, other parameters can be adjusted to modify the propertiesif it is desired to perform the process at a particular temperature.Typical reaction times for the third step in the process range from 1-4hours and, more preferably from 2-3.5 hours.

Once the precipitation step is completed the aluminosilicate product isisolated from the aqueous reaction medium. This is conveniently done byfiltration, for example, in a standard plate filter press.

Generally, the product is washed to remove impurities and, inparticular, unreacted metal silicate and sodium sulfate therefrom. Thetype and degree of washing will generally be dictated by the productspecifications and economic factors. Washing is generally done withwater, and preferably demineralized water, and repeated several timesuntil the concentration of dissolved salts in the wash water is reducedto a minimum. Once washing is complete a wet filter cake is obtained.

More preferably, washing of the filter cake is generally done withwater. After having reduced the concentration of dissolved salts in thewash water to a minimum, the filter cake can be washed with an ammoniumsalt solution, e.g. ammonium sulfate or ammonium chloride. This is donewhen a sodium-free aluminosilicate is required. To remove the excess ofammonium salts, the filter cake is washed again with water. Once washingis complete a wet filter cake is obtained, which is dried byconventional means. To remove ammonia from the surface of the driedaluminosilicate, the product can be calicined in air at elevatedtemperatures (300°-700° C.).

The filter cake is then broken up and dried by conventional means. Onedrying method employs a fluidized bed dryer and temperatures of130°-160° C. A more preferred drying method employs a flash dryer, aninlet temperature of about 350° C. and an outlet temperature of 120° C.

Once drying is complete, the dried product is mechanically broken intosmall particles by, for example, milling in a hammer mill and/or byslurrying the product and using a ball mill. The aluminosilicate isgenerally milled to an average particle size of 1-15 μm and, morepreferably, 4-12 μm. The resultant product may be dried and sold in bagsor can be slurried and transported in tanks.

The aluminosilicate product is useful in carbonless copy paper as apressure sensitive pigment, as well as in coatings and other typicalapplications of aluminosilicates. p The aluminosilicate product of thepresent invention contains at least 9 weight percent alumina, morepreferably from 9-15 weight percent alumina and, most preferably, 10-14weight percent of the aluminosilicate is alumina.

The aluminosilicate product has a BET surface area of 300-600 m² /g and,more preferably, the BET surface area is from 400-550 m² /g. Thealuminosilicate also has an average pore volume of of 0.2-0.5 ml/g.,and, more preferably, from 0.25-0.4 ml/g.

More preferred aluminosilicates are also characterized by having anaverage particle size of 1-15 μm and more preferably, 5-12 μm; a DBP oilabsorption of 50-200 ml/100 g and, more preferably, 80-150 ml/100 g; andthe pH of a 2% by weight solution of the aluminosilicate indemineralized water is 8.5-11.0 and, more preferably, 9-10.

The invention will be further illustrated by the following examples inwhich all percentages are percentages by weight.

Examples 1-21 and Comparative Examples A-P

Several different aluminosilicate products were prepared by essentiallythe same process varying only the dosing time, temperature, pH, SiO₂:Na₂ O molar ratio and washing conditions. The production process usedwas essentially as follows.

In a 20 liter RVS reactor, was placed 7 liters of demineralized water atthe desired reaction temperature (20° or 60° C.). To this water wasadded 500 grams of concentrated sodium silicate solution (27.5% SiO₂)whereby a pH between 10-11 was obtained. Thereafter, the pH was loweredto the desired pH (see Table 1) by addition of aluminum sulfate solution(8% aluminum oxide) over a period of about 20 minutes (about 225 gramsfor an SiO₂ :Na₂ O ratio of 3.3).

Thereafter, over the dosing period specified in Table 1, additionalaluminum sulphate (typically 2.6 kg of solution) and sodium silicatesolutions (typically 8.58 kg of a diluted solution containing 1/3waterand concentrated sodium silicate solution) were added to the reactorcontents. The sodium silicate solution was added at a constant rate andthe pH was held at the value listed in Table 1 by adjusting the rate ofaddition of the aluminum sulphate solution.

At the end of the dosing step, the precipitate was separated byfiltration and washed free of salts by repeated washings withdemineralized water. Finally, the aluminosilicate product was dried in aflash dryer at an inlet temperature of 350° C. and an outlet temperatureof 120° C. The dried product was milled in a hammer mill. The propertiesof the end products can be found in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                       SiO.sub.2 /                                                                       Surface                                                                           N.sub.2        DBP  pH                                  Dosing                                                                            Temper-   Na.sub.2 O                                                                        Area                                                                              Pore Particle  oil ab-                                                                            (2%-                                Time                                                                              ature     molar                                                                             (BET)                                                                             Volume                                                                             Size Alumina                                                                            sorption                                                                           solu-                          Example                                                                            (min)                                                                             (°C.)                                                                       pH   ratio                                                                             (m.sup.2 /g)                                                                      (ml/g)                                                                             d50 (μm)                                                                        (wt. %)                                                                            (ml/100 g)                                                                         tion)                          __________________________________________________________________________    1    120 60   7.5  3.3 419 0.47 5.0  11.6 156  9.3                            2     90 60   7.5  3.3 318 0.40 6.0  --   149  10.3                           3    191 60   6.5  3.3 454 0.31 7.26 11.2 112  9.7                            4    120 60   6.5  3.3 377 0.29 5.9  11.3 111  9.7                            5    120 60   5.5  3.3 446 0.27 11.2 11.3 --   9.7                            6    120 20   7.5  3.3 517 0.46 7.6  10.2 131  10.2                           7    120 60   4.5  3.3 393 0.21 11.8 11.4 --   9.3                            8    120 20   7.5  3.3 378 0.26 7.61 11.7 --   --                             9    120 60   6.5  3.3 444 0.33 6.42 10.8 114  9.6                            10    86 60   6.5  3.3 409 0.31 6.28 10.8 111  9.7                            11   191 60   5.5  3.3 460 0.27 7.42 10.7 100  9.5                            12    86 60   5.5  3.3 391 0.24 7.16 10.6 110  9.5                            13   429 60   5.5  3.3 357 0.22 7.35 10.6 --   9.2                            14   120 60   5.5  3.3 363 0.23 7.03 10.5 90   9.0                            15   120 60   6.5  3.3 411 0.33 5.98 10.5 118  9.2                            16   120 60   5.5  3.3 449 0.27 7.06 10.4 97   9.1                            17   191 60   4.5  3.3 444 0.25 7.39 11.0 78   8.5                            18   191 20   6.5  3.3 441 0.30 6.34 10.8 115  8.9                            19   120 60   5.5  3.3 509 0.34 6.28 10.9 113  8.7                            20   120 60   6.6  3.3 418 0.33 5.67 10.8 117  8.6                            21   120 60   6.6  3.3 365 0.33 6.35 10.6 123  9.1                            A    150 60   7.5  3.3 222 0.26 8.0  --   --   9.7                            B    120 60   7.5  2.0 62  0.10 6.6  --   112  9.8                            C    120 60   7.5  2.6 138 0.13 7.2  14.0 105  10.0                           D    120 20   7.5  2.0 178 0.18 5.7  16.0 99   9.9                            E    120 20   7.5  2.6 258 0.22 5.7  14.0 105  10.1                           F    120 20   7.5  2.6 257 0.28 10.7 12.8 135  10.2                           G    120 20   8 → 3.1                                                                     3.3 107 0.085                                                                              --   10.1 --   7.4                            H    120 20   3.9  3.3 199 0.13 --   13.9 --   5.5                            I    120 20   4.1 → 4.3                                                                   3.3 51  0.04 --   6.4  --   --                             J    429 60   6.5  3.3 259 0.20 5.87 10.7 103  9.4                            K    191 60   7.5  3.3 256 0.26 5.18 10.6 117  9.9                            L    191 20   5.5  3.3 256 0.16 5.47 10.6 68   8.8                            M    120 20   5.5  3.3 205 0.14 5.66 10.7 --   8.7                            N    120 20   6.5  3.3 273 0.20 6.36 11.1 82   8.6                            O    120 60   8.5  3.3 105 0.17 5.59 7.9  124  10.6                           P    120 60   7.5  3.3 283 0.39 6.2  11.0 139  10.1                           __________________________________________________________________________     Notes                                                                         .sup.1 Not alkalified                                                         .sup.2 8.9% SiO.sub.2 solution and washed for 2 days                          .sup.3 Process begun by adding sodium silicate solution to the aluminum       sulphate solution                                                             .sup.4 4% aluminum sulphate solution employed                            

The pore volume was measured using a modified version of ASTM.D4641-87.More particularly, instead of using the desorption isotherm, theadsorption isotherm was employed. Further, the calculations of porevolume were based on the assumption that the relative pressure (P/P_(o))was 0.97 rather than the 0.99 in the ASTM method.

In FIG. 1, the pore volume and surface area of the aluminosilicateproducts are plotted against the pH at which the precipitation reactionis carried out. This figure shows the clear improvement obtained whenworking at pH's of 4.4-7.7.

The foregoing detailed description and examples of the invention havebeen presented for the purposes of illustration and description only andare not to be construed as limiting the invention in any way. The scopeof the invention is to be determined from the claims appended hereto.

what is claimed is:
 1. A process for the production of anon-hydrothermally treated aluminosilicate containing at least 9 weightpercent alumina, having a BET surface area of 300-600 m² /g, and anaverage pore volume of 0.25-0.4ml/g; comprising the steps of:a)preparing an aqueous solution comprising at least one metal silicate andhaving an SiO₂ :metal oxide molar ratio of 2.8-3.5; b) adjusting the pHof said aqueous solution comprising at least one metal silicate with asufficient amount of an aqueous solution comprising at least onealuminum salt to produce an aqueous solution having a pH of 4.4-7.7; c)precipitating the aluminosilicate from the aqueous solution of step (b)by concurrently dosing to the aqueous solution of step (b) additionalaqueous solution comprising at least one metal silicate and having anSiO₂ :metal oxide molar ratio of 2.28-3.5, and additional aqueoussolution comprising at least one aluminum salt, in such a manner thatthe pH is maintained at 4.4-7.7, steps (a)-(c) being carried out at atemperature of 0°-80° C.; and (d) isolating said aluminosilicate.
 2. Theprocess of claim 1 which further comprises alkalifying the aqueoussolution of step (a) to a pH of 10-11 prior to carrying out step (b) ofthe process.
 3. The process of claim 1 wherein said aqueous solution ofat least one metal silicate comprises 0.1-20 weight percent of solidscontent, and said aqueous solution of aluminum salt comprises analuminum salt in an amount of 3-20 weight percent.
 4. The process ofclaim 1 wherein said aluminum salt comprises aluminum sulphate andwherein said metal silicate comprises sodium silicate.
 5. The process ofclaim 1 wherein step (d) comprises the step of isolating thealuminosilicate by filtration and further comprising the steps of:e)washing the aluminosilicate to remove substantially all residual metalsilicate and metal sulfate therefrom; f) drying the aluminosilicate; andg) reducing the altuminosilicate to an average particle size of 1-15 μm.6. The process of claim 1 wherein the aqueous solution comprising atleast one metal silicate is dosed in step (c) at a constant rate of0.1-10 weight percent per minute, based on the weight of the aqueoussolution of step (a), and the rate of addition of the aqueous solutioncomprising at least one aluminum salt is adjusted to maintain the pH ina range of 4.4 to 7.7.
 7. A non-hydrothernally treated aluminosilicatewhich comprises at least 9 weight percent alumina, and possesses a BETsurface area of 300-600 m² /g, and an average pore volume of 0.25-0.4ml/g.
 8. The aluminosilicate of claim 7 which has an average particlesize of 1-15 μm and a DBP oil absorption of 50-200 ml/100 g.
 9. Thealuminosilicate of claim 7 wherein the pH of a 2% by weight solution ofsaid aluminosilicate in demineralized water is 8.5-11.0.
 10. Analuminosilicate made by the process of claim
 1. 11. Carbonless copypaper which comprises the aluminosilicate of claim
 7. 12. Thealuminosilicate of claim 10 which comprises at least 9 weight percentalumina and possess a BET surface area of 300-600 M² /g, and an averagepore volume of 0.25-0.4 ml/g.